This invention relates to sealing a semiconductor die edge, and more particularly to laser CVD sealing a semiconductor die edge.
A semiconductor die is subject to reliability failure if contamination from the outside world enters the device. One likely entrance location for contamination in a semiconductor die is the edge of the die. Semiconductor manufacturers typically fabricate a diffused line or region around the edge of the die to lessen the possibility of this form of contamination. The diffused line or region may also be biased to ensure entrapment of contamination in the diffused region.
A protective overcoat may also be placed over the die to prevent contamination from entering the die through the top surface. The protective overcoat extends past the die edge to help the diffused region capture the contamination. But even these precautions will not prevent contamination from entering the active region of the die through irregularities in the diffused line or region.
Irregularities are introduced into the die when the slice containing the die is scribed and broken. The scribe operation is a rough mechanical procedure that can damage the protective structures used to prevent contamination from entering the die from the die edge. The damage generally manifests itself in the form of cracks and nicks in the protective structures. Normal final testing may fail to detect cracks which, unfortunately, show up after the die has been in the field for some time.
Incidental field failures may also occur when bond wires droop during assembly. The bond wire may get close or electrically contact the die edge altering the signal to the die by shorting the die edge.
What is needed is a method to prevent contamination from entering a die through cracks in the edge of the die. What is also needed is a method to prevent bond wires or bond tracks, which run across the die edge, from shorting to the die or one another due to conduction through the die.
In accordance with one embodiment of the invention, a die is enveloped by an ambient gas that will react to the presence of a particular wave length of light. A laser beam is focused on the edge of the die. The gas undergoes a photo chemical or pyrolytic reaction on the die edge to deposit a dielectric coating. The laser beam or the die is rotated until the dielectric coating covers the entire die edge. The dielectric coating acts as a seal that is impervious to water and other contamination that can reduce the die reliability. The dielectric coating also electrically insulates the die from its surroundings.